This invention relates generally to electron beam apparatus of the kind in which an electron probe, constituted by a beam of electrons, is caused to impinge on a specimen under examination and information about, for example, the voltage distribution of the specimen surface is obtained by using a detector, including an electron collector, to pick up electrons emanating from the specimen.
Electron beam apparatus of the kind in which or for which the present invention may be used include general purpose scanning electron microscopes but also special purpose apparatus particularly adapted for inspection, quality control and fault diagnosis of integrated circuits.
It is generally known to employ an electron collector which collects secondary electrons emitted from the specimen, mainly as a function of the potential at the point on which the electron beam impinges, so as to develop an output signal which according to the mode of operation chosen for the electron beam apparatus can be used to derive, for example, a voltage contrast image or (particularly if stroboscopic scanning is used) information concerning the dynamic behaviour of the specimen under test. It is known to employ an electron collector which includes an extraction grid which may overcome field distortions above the surface of the specimen and also a control grid which can form a potential barrier of variable height to discriminate between secondary electrons emanating from regions of the specimen's surface of different potential. It is also known to employ a scintillator to collect the secondary electron current and to provide some discrimination between two secondary electrons emitted from the specimen and high energy reflected primary electrons.